Coagulase-negative staphylococci (CNS) are an important cause of nosocomial bacteremia and they are frequently considered as contaminants of blood-cultures. From October 1990 to September 1992, 300 positive blood-cultures for CNS at the Hospital São Paulo were studied and 141 CNS bacteremias were characterized as nosocomial bacteremias. Clinical and microbiological criteria were defined to differentiate between true CNS bacteremia and contaminated cultures. Only 20.6% of the CNS nosocomial bacteremia were considered as true bacteremia. Most of the CNS true nosocomial bacteremia were detected among newborns admitted to the neonatal intensive care unit; the presence of intravascular catheter and parenteral nutrition were significant findings. We did not detect significant difference between true nosocomial bacteremia and contaminated cultures regarding to resistance to oxacillin and SLIME production. The clinical criteria and the positivity of the blood-cultures up to 48 hours after incubation, utilized in our definitions, were useful parameters to characterize the CNS true nosocomial bacteremia.